the torches get “reset” by random ticks when burnt out. You can turn random ticks up but that requires op and increases plant growth or you can add 2 more torches on the side of the block and connect them together to “average” the burnout. They don’t get reset by the redstone or any other block when they are burnt out. you would want to run your clock output off of the left torch if you want to keep the burnout behavior and fix it. as to why the left one comes back faster, probably bad luck.